Absorbent for refrigerating apparatus



Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE HARRY F. SMITH, OF DAYTON, OHIO, ASSIGNO R TO FRIGIZPAIBE CORPORATION, OF

' DAYTON, OHIO, A CORPORATION OF DELAWARE ABSORIBE'NT FOR REFRIGERATIN G APPARATUS No Drawing. Application filed May 30,

This invention relates to solid absorbent materials for refrigerating apparatus of the absorption type.

It is one of the objects of the invention to provide a solid or dry absorbent material which is mechanically stable, that is one which does not materially change its apparent physical or mechanical form or migrate from one place to another over long periods of operation.

Another object is to provide an absorbent material or structure in which the individual particles of the the material are held together in such a manner as to permlt expansion and contraction of the particles themselves and movement incidental or necessary thereto, of the particles or small aggregates thereof without disturbing large aggregates of particles or the mass of material as -a whole.

Another object is to provide an absorbent; material having a large amount of surface exposed to refrigerant, and a large number of gas passages throughout the material so as to assure free passage of. refrigerant into and out of the mass of material.

Further objects and 'a dvantages of the present invention will be apparent from the followin description and claims.

Dry asorption refrigerating systems using a solid or dry absorbent material for the refrigerant have heretofore been proposed, for example systems usingcalcium chloride for alternately absorbing and evolving ammonia. Such systems have not proved Wholly successful due, in part at least, to the fact that calcium chloride (and substances of like nature which constitute the chief absorbents for ammonia) expand tremendously upon absorbing ammonia, and contract or shrink correspondingly upon evolving ammonia. This results in an inherent mechanical instability of the structure of the mass of absorbent material which prevents it from being kept in any constant form or shape, prevents it from being kept in satisfactory heat exchange relation with heating and cooling devices essential to the system, and causes the particles to migrate during evolution and 50 absorption so as to produce progressive con- 1929. Serial No. 367,156.

centration of particles in certain spaces at the expense of other spaces. Such migration and concentration frequently develops sufiicient force to destroy containers or generator-absorbers in which the material is used. 56

My invention is concerned with eliminating these phenomena and producing a solid absorbent structure which will retain its size, shape and position under all conditions of the cycle of operation and Will not exert de- 60 structive forces upon vessels in which it is confined. v

I prefer to use as absorbent strontium chloride. This material is very similar to calcium chloride as regards its aflinity for 6a ammonia, its formation of definite chemical compounds known as addition products or addition-compounds with ammonia, and its behavior during the absorption and evolution of ammonia. Strontium chloride, SrCl absorbs ammonia to form anyone of the following addition-compounds, ammoniates, or ammineszStrontium chloride 1- ammine, SrCl NH strontium chloride 2- ammine, SrCl 2NI-I and strontium chloride S-ammine, SrCl .8NH The manner in which. the material is converted from one ammine to another to absorb or evolve ammonia and the'conditions necessary to such conversion are known physical-chemical data, being mentioned for example in the patent to F. G. Keyes, 1,698,847, January 15, 1929, and in my companion application for refrigerating apparatus, Serial No. 367,157, filed of even date herewith.

Pure anhydrous strontium chloride is a very fine powder or dust. A mass of this material consists of individual extremely minute particles contacting with each other at isolated points and thus providing free spaces between the particles. The mass is similar in type to loose broken gravel. When this material is exposed to ammonia under the proper temperature and pressure conditions, the ammonia gas enters the spaces between the particles and each particle is converted into a particle of the particular ammoniate which corresponds to the pressure and temperature. A particle of any ammoniate is larger than a particle of a lowerorder ammoniate or of the pure strontium chloride. Consequently whenever the material absorbs ammonia the individual particles swell, and if the spaces'between them are not suflicient to hold the enlarged particles,.the body as a Whole must swell or large aggregates of particles must be moved. If

the material is confined so that it cannot swell,-

extremely high pressures are developed, which may distort or destroy containers, and

, in any event the material may pack so as to obstruct the gas passage between the particles and prevent free ingress or egress of ammonia.

As a specific example, SrCl .8NH when in one" condition which is considered a well packed powder, has a bulk density of 43 pounds per cubic foot. In this the free gas space is about 50% of the total. Assume that a quantity of this material is placed in an ordinary laboratory glass test tube and he-at ed to drive off ammonia and convert the material 'into SrC1 .NH The free gas space would become about 80% of the total ifthe apparent volume of the entire body remained the same. However, the particles may fall into these larger spaces between them caus-' ing the entire mass to shrink, crack and settle until the volume of the entire body is reduced, frequently as much as 20%. Upon subsequently absorbing ammonia, the particles again tend to expand, but the entire body of material is not restored to its former size,

. shape, or position because the movements of tion in which the mass is free to expand) to the spaces between the particles blocks the pack together and block the tubelike a tightly fitting cork, so that the top layer is not moved by the pressure of the expanding particles beneath it. This will result in the development of high pressure beneath the surface which has two necessary results, the one pressing of the particles into the spaces so as to pack the powder into a chalk-like mass, and the other exertion of considerable force on the container. Both of these results are undesirable, the first because the filling of passages for the ingress and egress of ammonia gas, and the second because it may" destroy the container. Subsequent alternate evolution and absorption of ammonia will cause the powder to progressively settle and progressively pack until the resistance to expansion developed at the top of the mass may cause the expansion of material confined below the surface to burst the test tube.

I ha e discovered that the particles of stronti chloride or other absorbent materials having similar characteristics can be agglomerated in such a manner as to prevent the alternate expansion and contraction, as well as progressive concentration of the mass of material as a whole. This is accomplished by mixing with the powdered material a small quantity of a suitable viscous liquid and distributing the liquid throughout the entire mass so that each particle is wet by a thin film. The liquid used must obviously be of such character as to wet the particles of the absorbent material with which it. is employed. hen the liquid is thoroughly distributed throughout the pow der, it forms a thin film over the surface of each individual particle, and where the particles contactwith each other the liquid film becomes thicker in the inter-spaces or corners immediately surrounding the points of contact. This is due to the known phenomena of capillarity and surface tension. Where the particles are in contact with each other the thicker film of liquid will cause the particles to adhere together. While the liquid employed must be sufiiciently viscous to cause the particles to adhere, yet it must not be too viscous to prevent its flowing into the corners around the points of contact. Likewise,

the liquid must be of such nature as to permit the refrigerant to pass through the films of liquid to the individual particles in order to reach the strontium chloride. Preferably the liquid is one in which the refrigerant is soluble. Also the liquid should be of such nature that it reduces friction between particles but yet does not remove the friction altogether. In other words, the liquid film which ties together adjacent particles must shear without tearing apart so that the particles may be moved with respect to one another and yet be held together. The resulting structure is analogous to what a popcorn ball would be if bound together with syrup which did not congeal.

As examples of liquids suitable for this purpose may be-mentioned lithium nitrate and white mineral oil of the character of that marketed under the trade name of Nujol. I prefer to use lithium nitrate. This material is similar to strontium chloride in that it is normally a solid which absorbs ammonia, but

different in that in absorbing ammonia, it forms a liquid rather than a solid throughout the temperature and pressure range in which the strontium chloride forms the ammines mentioned. The liquid formed is stable and of practically constant physical characteristicsthroughout the operating range of the strontium chloride. Lithium nitrate is given as an example of one substance which has the necessary characteristics to form the desired agglomeration, but other materials may be employed within the scope of my invention. My absorbent structure may be prepared b mixing lithium nitrate wfith strontium c loride in such proportions as to give from 4 to 10% and preferably 5% LiNO in (LiNO +SrCl This may be accomplished, for example, by mixing anhydrous strontium chloride powder with anhydrous lithium nitrate owder to form a substance containing lithium nitrate to the extent of from 4 to 10% (preferably 5%) of the total. After these two substances have been thoroughly mixed the material is cooled in the presence of ammonia gas so as to cause the material to absorb the ammonia forming the strontium chloride 8-ammiine. Upon ex osure to ammonia the lithium nitrate absor ammonia forming a liquid which has the characteristics mentioned above. This material is then ground to a fine powder which to the naked eye appears dry but under the microscope has the appearance of wet snow, and is charged into a generator-absorber such as shown in my companion application referred to. Thereafter the material is heated and cooled to evolve and absorb ammonia for several successive cycles. Upon the first evolution of ammonia the material may have a slight tendency to settle, this being undoubtedly due to imperfect distribution of the lithium nitrate. The subsequent periodic absorption and evolution of ammonia serves to distribute the lithium nitrate and results in a mass of 'material which to the naked eye has the apslightly damp packed powder analogous to packed molding sand. Under the microscope however, the thin films of liquid may be discerned. The mass of powder retains its form during subsequent absorption and evolution of ammonia.

A study of the material after it has been cycled sufficiently to distribute the lithium nitrate and form a mass as described indicates that the films of liquid hold the particles together with suflicient free gas =pace between them to provide a system of passages for conducting ammonia gas to all of the particles. This space is suflicient to permit the expansion of the individual particles upon absorption of ammonia into the spaces between particles without blocking the spaces, without expanding the mass of the material as a whole and without exerting any great force upon the walls of the container. Likewise upon evolving ammonia, the liquid films hold the individual particles in their approximate relation without falling into the spaces. During expansion and contraction the individual particles must move somewhat with reference to each other, but as has been stated, the liquid films permit this movement while holding the particles together. The liquid in lubricating the particles or reducing the friction of the particles in moving over one another, reduces the pressure required to move the ammonia throughout the system,-

and permits the articles to slide overone another in expan ng and contracting without packing or materially changing the's't'ructure as a whole.

While the form of embodiment of the invention as herein disclosed, constitutes a a within the sco e of the claims which follow.

What is claimed is as follows:

1. An absorbent for refrigerant in refrigerating a paratus of the absorption type consisting o a powdered solidmaterial having the property of entering into chemical combination with the refrigerant, the particles changing volume when so combining with the refrigerant, the particles of the powder being individually wet and bound together with a thin film of liquid, said liquid being permeable to the refrigerant and stable throughout the tem rature and pressure range to which the a sorbent is subjected.

2. An absorbent for ammonia in refrigerating apparatus of the absorption type consisting of a solid material having the pro erty of forming definite addition-compounds with ammonia, the particles changing volume when so combining with the refrigerant, the particles of the solid being individually wet and bound together with a thin film of liquid, said liquid being permeable to the refrigerant and stable throughout the temperature range to which the absorbent is subjected.

3. An absorbent for refrigerant in a refrigerating a paratus of the absorption type consisting o a solid material having the propert of entering into chemical combination Wit the refrigerant, the particles changing volume when so combining with the refrigerant, the particles of the solid being individuall wet and bound together with a thin film 0 liquid, said liquid being permeable to the refrigerant and stable throughout the temperature and pressure range to which the absorbent is subjected.

4. An absorbent for refrigerant in a V refrigerating apparatus of the absorption type consisting of a solid material having the property of entering into chemical combination with the refrigerant, the particles changing volume when so combining with the refrigerant, the particles of the solid being individuall wet and bound together with a thin film 0 liquid in which the refrigerant is soluble, said liquid being stable throughout the temperature and pressure range to which the absorbent is subjected.

5. An absorbent for refrigerant in a refrigerating a paratus of the absorption type consisting o asolid material having the property of entering into chemical combination with the refrigerant, the particles changing volume when so combining with erating apparatus of the absorption type consisting o a solid material having the property of entering into chemical combination with the refrigerant, the particles changing volume when so combining with the refrigerant, the particles of the solid being individually/wet with a film of liquid sufficiently viscous to cause the particles "to adhere to one another and sufliciently thin to leave free gas space between the particles for the passage of refrigerant gas throughout the mass of material, said li uid bein permeable to the refrigerant an stable t roughout the temperature and pressure range to which the absorbent is subjected.

' 7. An absorbent for refrigerant in a refrigerating apparatus of the absorption type consisting of a solid material having the property of entering into chemical combination with the refrigerant, the particles changing volume when so combining with the refrigerant, the particles of the solid being individually wet with a film of liquid suflicient- 1y viscous to cause the particle's'to adhere to one another and sufliciently thin to ermit the passage of refrigerant gas throug the film to the particles, said liquid being permeable to the refrigerant and stable throughout the temperature and pressure range to which the absorbent is subjected.

8. An absorbent for refrigerant in a refrigerating apparatus of the absorption type consisting of a solid material having the property of entering into chemical combination with the refrigerant, the particles changing volume when so combining with the refrigerant, the particles of the solid bein individually wet with a film of liquid suciently viscous to cause the particles to adhere to one another and of such characteristics as to permit the passage of refrigerant through the film to the particles, said liquid being stable throughout the temperature and pressure range to which the absorbent is subjected. w

9. An 'absorbent for refrigerant'in refrigerating apparatus of the absorption type consisting of a body of solid material capable of forming with the refrigerant addition-compounds of high and low order, the particles changing volume when so combining with the refrigerant, the particles of said solid being held together with sufficient free gas space between them to permit the particles to expand in forming addition-compounds of high order and to contract in form-' ing addition-compounds of low order without a body of solid material capable of tion-compounds of high order and to contract '7 in forming addition-compounds of low order without materially changing the total volume.

of the mass, said liquid being permeable to the refrigerant and stable throughout the absorbent is subjected.

11. An absorbent for refrigerating apparatus consisting of solid material capable of temperature and pressure range to which the v absorbing and evolving refrigerant, said material belng characterized by a tendency to expand uponabso'rbing and to contract upon evolving the refrigerant, and the particles of the solid being-held together by adhesive liquid films, the liquid belngsof such nature as to reduce friction between particles in their movement during expansion and con traction, said liquid being permeable to the refrigerant and stable throughout the temperature and pressure range to which the absorbent is subjected.

12. An absorbent for refrigerating apparatus consisting of solid material capable of absorbing and evolving refrigerant, said'materi'al being characterized by a tendency to expand upon absorbing and to contract upon evolving the refrigerant, and the particles of the solid being held together by adhesive liquid films, the liquid being of such nature as to permit particle movement without breaking of the liquid films between adjacent particles during expansion and contraction, said liquid being permeable to the refrigerant and stable throughout the temperature and pressure range to which the absorbent is subjected.

13. An absorbent sorb refrigerant in refrigerating apparatus consisting of a mixture of two' absorbent substances each adapted to absorb refrigerant, one of the substances forming a solid product with the refrigerant and the other forming a liquid product. 1

14. An absorbent material adapted to absorb refrigerant in refrigerating apparatus consisting of a mixture of two absorbent substances each adapted to absorb refrigerant, one of the substances being always a solid,

and the other being adapted to form both solid and liquid phases.

15. An absorbent for ammonia in refrigerating apparatus of the absorption type consisting of a solid material capable of entermaterial adapted to ab-' 1 ing into chemical combination with ammonia, and of lithium nitrate to the extent of from 4 to 10% of the total.

16. An absorbent for ammonia in refrigerating apparatus of the absorption type consisting of a solid material capable of entering into chemical combination with ammonia and lithium nitrate .to the extent of approximately 5% of the total ammonia-free absorbent material.

17. An absorbent for ammonia in refrigerating apparatus of the absorption type consisting of a mixture of strontium chloride and lithium nitrate.

18. An absorbent for ammonia in refrigerating apparatus of the absorption type consisting of a mixture of strontium chloride and lithium nitrate, the lithium nitrate being from l to 10% of the total ammonia-free absorbent material.

19. An absorbent for ammonia in refrigerating apparatus of the absorption type consisting of a mixture of strontium chloride and lithium nitrate, the lithium nitrate being approximately 5% of the total ammonia free absorbent material.

In testimony whereof I hereto afiix my signature.

HARRY F. SMITH. 

